[Data] dataset.write_iceberg to support upserts

[gero90]

Description

As pyiceberg now supports upserts (example), it would ideal to support the 3 modes in Ray Data (append, overwrite, upsert).

Related: This one is adding overwrite mode #51951

Use case

With upserts, the ray data capabilities would be greatly extended, reducing the need of post-processing of append-only tables

[richardliaw]

This makes sense. We recently added more modes to parquet as well. Would you be willing to contribute here?

[my-vegetable-has-exploded]

I'd like to try it later！

[gero90]

it seems the overwrite PR got staled: #51951
should this one be after that one, or deal with in in parallel / join both approaches?

[goutamvenkat-anyscale]

Upserts are now supported as of aecff3c